U.S. Pat. Nos. 2,722,398; 3,684,238; 4,647,008; and 4,852,853 disclose pressure balanced solenoid controlled valves for controlling the flow of hydraulic fluid in hydraulic control systems for controlling a hydraulic device. The use of solenoid controlled valves requires rigorous manufacturing tolerances when the valving element is a spool. In the aforesaid arrangements the spool is replaced by a poppet valve which enables the valves to operate in contaminated environments while maintaining clearance tolerances comparable to spool type control valves.
U.S. Pat. No. 3,606,241 discloses a poppet type valve with a spindle which is coupled to the armature by a coupling spring so that valve opening will be independent of energization current to a solenoid coil.
In the aforesaid arrangements, provision for pressure balancing is accomplished by providing a direct path through the poppet valve stem. While suitable for their intended purpose, poppet type valves will not provide pressure control which varies linearly in accordance with the position of an armature within a solenoid coil.
A particularly desirable form of valve for linear pressure control is a needle valve movable concentrically within a control orifice to interact therewith to precisely control pressure for different positions of the needle within the orifice. However, such valve arrangements do not provide enough cross sectional material in the valve element or valve stem to form a pressure balancing path through the valve element and the armature to balance pressure thereacross.